Process of manufacturing silicon-steel products.



orro n. cunnmsnnm, or LnEcHBUne,imnnsrnvnnrn,nssienon, BY MESNE .AS-

UNITED sir-Arias PAEENT OFFICE SIGNMEN TS, TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

rnocnss or MANUFACTURING sIL eoN-sTEEL PRODUCTS.

Specification. of Letters Patent.

Patented'Dcc. 1c, 1913.

No Drawing. Gontinuation of application Serial No. 620;478, filed April 1-1, 1911. This application filed December 13, 1911.

To all whom it may concern lie it known that I, O'rro H. CUNruNo- HAM, a citizen of the United States, reslding at Leechburg, in the county of Armstrong and State of Pennsylvania, have invented new and useful Improvements in Processes for Manufacturing Silicon-Qteel Products, of which the following is a specification, the sa-me'being a continuation in part of the specification of my prior application, Serial NQBQOA'ZS, filed April 11, 191 1.

My invention relates to the manufacture of'sheets, plates, or other products composed of silicon steel.

@ertain parts of electrical apparatus, havingalternating magnetic fields, for example, transfiormer cores, armaturecores, pole pieces, and magnetic poles of various kinds, are preferably or necessarily of a laminated structure, being composed of plates or laminae ofsheet' iron or steel. All sheet metal for such and analogous purposes should possess a high degree of magnetic permeability, and alow de cc of magnetic hysteresis, and be physical y very strong and pliable. Some sheet iron and steel, notably that employed in transformer cores and to a lesser extent that used in alternating current gencraters, must be characterized by low hysteresis loss. In transformer cores especially, the hysteresis loss is a most important consideration; but it is desirable to combine low hysteresis loss with high permeability and the physical desiderata hereinbefore mentioned. Transformer sheets must also be non-aging, that is, they should not deteriorate withage, moreespecially with respect to hysteresis loss. It has been found that steel having a high silicon content, but otherwise as free as commercially practicable from all other elements save iron, furnishes, with proper care, a sheet which meets all the above described requisites in 'aremarkable degree.

For every ingot of steel, there exists a maximum of physical excellence that is rend'ered possible by its nature or chemical composition. That maximum of excellence is developedby proper treatment; while, on the other hand, the product may be ruinedby faulty treatment, however excellent the ingot may have been. Similarly, a certain minimum hysteresisloss is possible for any ingot of silicon steel; but improper rolling,

Serial No. 665,434.

heating, or other treatment will develop therefrom a sheet of very high hysteresis loss. By my invention I am enabled to pro duce silicon sheet steel of much lower hysteresis loss than would be possible inany 'other way known to me, the improvement due to my invention being definite and well marked, amounting to as much as 10 to 15%. Moreover, my improved process enables me to treat sheets that have already been brought to the minimum hysteresis loss possible under existing methods of sheet rolling, and to effect in them the marked improvement of hysteresis quality above ment1oned,'an d this altogether separate from the decrease in eddy loss due to reduction in li 'l nder common sheet or tin mill practice a run-over pack is produced from one or more sheet-bars by suitable heating, rolling, pairing, matching, doublin or otherwise ma-nifolding, any or all of these steps being taken in an desired number or combination. This pack is usually four-ply, and approximately the full length and thickness of the finishedpack. This run-over pack is then usually doubled, given the finishing heat in the sheet furnace and then rolled out to length. The result so far is a finished pack, which has the same length and thickness as the run-over pack; but, on account of the doubling, has twice as many ply. The fi'nished pack is then sheared, opened, and annealed, preferably box-annealed, and sometimes cold rolled.

According to my new process, silicon steel sheets may be prepared substantially accord in to the usual method, or in any other suitable manner, as, for example, that above described as far as and including the ordinarypfinishing heat. When my method is practised as a step in reducing sheets to the finished gage, T givethe pack the usual number of finishing passes less one. The pack, which under the customary practice is still hot enough to finish without further heat ing, is charged at once into a sheet furnace or its equivalent, there to remain untilraised toa suitable temperature not lower than red, or to any heat which in connection with the subsequent rolling will impart to the sheet its desired quality. After being so reheated the pack is withdrawn from the furnace and proinptly'given one or two passes in a sheet mill. It is believed that the final pass or passes should be of such number or so conducted that the sheet is subjected to pressure until it has cooled to a point at which no further molecular change can occur. It has been observed in the practice of my invention that good results are obtained if the reheating and subsequent rolling be so conducted that the sheets after such rolling have a temperature higher than that of sheets produced in the usual manner. After cooling, shearing, and opening, followed by cold rolling, if desired, the silicon steel sheets rolled according to my process just described, may be and preferably should be annealed in any approved manner, but boxannealing is preferred.

iiy process, therefore, consistsin rolling silicon steel sheets or their equivalent from sheet-bars or other product according to any rational or approved practice up to and including, if desired, all the finished passes; in giving the resultant pack, plate, or equivalent, a reheat to the desired temperature; and in immediately giving the reheated pack, plate or sheet, a pass through sheet rolls. The final pass of the sheets or plates so heated should be accompanied by such a roll pressure as will put the steel in such a potential condition that, when it is subsequently annealed in the usual or other manner, it will have its hysteresis quality much improved over the hysteresis quality which would be due to the usual finishing hereinbefore described.

My process may be applied to silicon steel sheets that have been finished according to usual practice and have reached the maximum excellence commercially possible for sheets finished according to the said practice. By my process such sheets, after receivin a reheat are either sin l or in loose or tight packs of two or more sheets, given a pass through the sheet rolls, care being takenthat at the time of rolling the sheets have a temperature which in connection with the rolling will produce the result desired. a I do not limit my invention to giving the steel one pass after it has received my special reheating step, as good results may be obtained by more than one pass, and while I have stated that I prefer to omit one of the finishing passes to which sheets are subjected under ordinary or preferred mill practice, before giving the sheets my special reheat, a larger number of the finishing passes may be omitted, if the preceding finishing passes have brough the metal into such a condition that the subsequent steps of my process will. give 'themetal its desired characteristics.

I have stated herein that the silicon sheets are reheated to a suitable temperature before giving them the subsequent pass or passes as herein stated. The temperature of the reheated sheets has been observedto be usually orange; but in a number of instances this temperature has been observed to be above and below orange with better results than were practicable with the old practice. As stated hereinbefore, the sheets after having been given all but the last one or two finishing passes are hot enough to finish according to usual methods without reheating; but are according to my method raised to ahigher temperature before being given the final finishing pass or passes. This higher temperature has a wide range limited on the minimum side by the temperature at which the potential condition herein specified will be secured. Satisfactory results have been obtained when the sheets after the final finishing pass ranged in color from low orange to bright red, and satisfactory results have been obtained when the sheets have been finished above low orange and below bright red.

The degree of heat which it is believed to behest for my reheating is at or above that temperature at which the former structure of the steel disappears or is'modified according to the laws of metallography. By the rolling which the silicon sheets receive after they have been reheated, they are made to undergo Work while cooling to, or to the vicinity of, the critical point or point of recalescence. By raising the temperature of the sheets high enough to obliterate or modify previous structure, and keeping them under work while cooling to, or to the vicinity of, the critical point, a condition most favorable to the production of the highest potential quality, or the lowest potential hysteresis loss in the finished product is obtained.

Besides the lowering of hysteresis losses brought about by my process, I obtain, ac-

cording to this process, sheets which are exceedingly strong and free from brittleness, and physically much better adapted for the construction of electric apparatus, such as transformer cores, alternating current generators, or other apparatus having alternating magnetic fields, and the like than any other silicon steel sheets known to me.

Silicon sheets manufactured in accordance with the principles of my process are very desirable for the construction of resistance grids by stamping because they possess a higher ohmic resistance than grids which could be prdduced by the usual processes of treating such sheets.

Before the sheets which have been given a pass or two after giving them my final reheat are used for electrical purposes, such as transformer cores, alternating current generators, resistance grids, and the like, they must be annealed, preferably in anneaL ingboxes, to develop in them the qualities hereinbefore stated to be desirable for trans former cores alternating current generators, resistance grids, etc. This annealing does not necessarily immediately follow the final rolling in the finishing rolls but may be.

preceded by shearing, opening and the like. This should be taken into account in construing the claims.

The word sheet used in the description and claims is to be construed as covering all sheet-like bodies although they may be technically given other names, such as plates. I

1. The process of finishing silicon sheet steelwhich consists in giving the sheets finishing passes in rolls, and intermediate some of the fiuishing passes giving the sheets a reheat.

2. The process which consists in completing the final mechanical reduction of silicon sheet steel above the ordinary finishing temperature.

3. The process which consists in completing the final mechanical reduction of silicon sheet steel at orange heat.

4. The process which consists in reheating a pack of silicon sheet steel to a temperature not lower than the ordinary reheating temperature and quickly passing the pack between reducing rolls so as to discharge the'pack at a temperature above the ordinary discharging temperature.

'5. The process which consists in so reheating and passing a pack of silicon steel sheets between reducing rolls as to discharge the finally reduced product above the ordinary discharging temperature.

6. The process which consists in heating silicon sheet steel to a temperature not lower than the ordinary reheating temperature and giving to it one final reducing pass between rolls.

7. The process of treating silicon steel sheets after they have been heated for the finishing passes and subjected to the action of the finishing rolls, which process consists in reheating the sheets to not lower than a red heat, and subjecting the reheated sheets to not more than twodraft passes through finishing rolls.

8. The process of treating silicon steel sheets after they have been heated for the finishing passes, which process consists in finishing the sheets in finishing rolls with the exception of not more than the last two passes, reheating the sheets to not lower than a red heat, and subjecting the reheated sheets to not more than two draft passes through finishing rolls.

9. The process of treating silicon steel sheets after they have been heated for the finishing passes and subjected to the action of finishing rolls, which process consists in reheating the sheets to not lower than a red heat, subjecting the reheated sheets to not more than two draft passes through finishi-ng rolls, and annealing the sheets.

10. The process of finishing silicon sheet steel which consists in giving the sheets finishing passes, reheating the sheets, and rolling the reheated sheets until they have attained a temperature not lower than red.

1].. The process of finishing silicon sheet steel which consists in giving the sheets finishing passes, reheating the sheets, and cooling them to not lower than red by the action of finishing rolls.

12. The process of treating silicon steel sheets after they have been heated for the finishing passes and subjected to the action of finishing rolls, which process consists in raising them to the temperature at which the previous structure is modified, causing them to undergo work during cooling to the critical point, and annealing the sheets.

13. The process of treating silicon steel sheets after they have been heated for the finishing passes and subjected to the action of finishing rolls, which process consists in raising them to the temperature. at which the previous structure is modified, and cans ing them to undergo work during cooling to the critical point.

14. The process of treating silicon steel sheets after they have been heated for the finishing passes and subjected to the action of finishing rolls, which process consists in reheating the sheets to not lower than a red heat, subjecting the sheets to the action of rolls, and annealing the sheets, the working of the sheets in the rolls being under such pressure and for such a time as will place the metal in that potential condition which upon subsequent annealing will develop sheets of desired magnetic characteristic.

15. The process of finishing silicon sheet steel, which consists in completing the final mechanical reduction of the sheets at about the critical point.

16. The process of finishing silicon sheet steel, which consists in heating the sheets to not lower than the ordinary reheating temperature and giving to them a final reducing pass. between rolls so as to be discharged at about the critical point.

17. The process of making silicon sheet steel from the ingot, which consists in reducing the ingot to sheet form in any ordinary manner until the sheets of a pack have attained nearly but not quite the required thinness, then reheating the pack to a temperature not lower than the ordinary reheating temperature and then reducing the sheets to the desired thinness by one or two passes between suit-able rolls so as to discharge the'pack at about the critical point.

18. The process which consists in completing the final mechanical reduction of silicon sheet steel at about the temperature of recalescence.

19. The process which consists in heating- I steel from the ingot, Which consists in re ducing the ingot to sheet form in any ordinary manner until the sheets of a pack have attained nearly but not quite the reouircd thinness, then reheating the pack to a temperature not lower than the ordinary reheating temperature and then reducing the sheets to the desired thinness by one or two passages between suitable rolls so as to disa charge the pack at about the temperature of recalescence.

Signed at Pittsburgh, Pa, this 11th day of December,-19l1.

OTTO H. CUNNINGHAM.

Witnesses 1 ALICE E. DUFF, ELYA STANTCK 

